Papers by Author: Milena Pavlíková

Abstract: Residual parameters of Ultra High Performance Concrete (UHPC) exposed to high temperatures were experimentally accessed. The UHPC was provided by hybrid fibre reinforcement based on polyvinyl alcohol (PVA) and steel fibres. Among the studied material properties, bulk density, matrix density, total open porosity, pore size distribution, water vapour transmission and liquid water transport properties were examined. The UHPC samples were exposed to the temperatures 400 °C, 600 °C, 800 °C, and 1000 °C respectively. For comparative purposes, the reference UHPC samples cured at laboratory temperature were tested as well. Based on the obtained results, correlation between concrete structural changes and tested parameters was found out. The applied temperature load highly affected the concrete porosity, pore size, and thus both liquid and gaseous moisture transport parameters. Disintegration of concrete structure, colour change, cracking, damage of steel fibres (melting), and failure of their cohesion was apparent from optical microscopy analysis.

Abstract: Sulphate attack of concrete and cement composites comprises sulphate ions migration into the material porous space and their following reaction with hydration products in the presence of water. Newly formed compounds initiate filling of porous space and volume expansion. Sulphate corrosion phenomenon still belongs to the main mechanism affecting the durability and service life of concrete structures. This paper deals with the investigation of sulphate resistance of two types of High Performance Concrete (HPC) exposed for 168 days to sodium sulphate water solution and reference environment of distilled water. Corrosive action is monitored at chosen time periods non-destructively, i.e. using measurement of length and mass changes, basic physical characteristics and dynamic moduli. Additionally, destructive tests of mechanical parameters are realised. For samples immersed in distilled water, improvement in mechanical strength is observed for the both studied HPCs. In case of HPC C I containing crushed aggregate, the improvement of mechanical resistivity is observed for samples exposed to sulphate solution for 140 days only. For other researched period of sulphate exposure, mechanical strength decreased in comparison with the reference values. On the other hand, HPC C II exhibited mechanical resistivity to sulphate action in all examined time periods of sulphate solution exposure.

Abstract: Properties of a new type of sandwich composite based on magnesium board, silica aerogel thermal insulation layer, and water vapour barrier are experimentally analysed in the paper. For the basic characterization of the studied material, bulk density, matrix density, and total open porosity are measured. Among the thermal properties, thermal conductivity, thermal diffusivity, and volumetric heat capacity are accessed. Water vapour transmission properties are determined using the dry-cup and wet-cup arrangements of the cup method. In order to describe the liquid moisture transport, water absorption coefficient and apparent moisture diffusivity are calculated based on the data obtained from the free water intake experiment based on the sorptivity concept. Ability of the tested material to accumulate water vapour is described by the sorption and desorption isotherms measured using a dynamic vapour sorption device. Mechanical resistivity of the tested composite is characterized by its compressive and flexural strength. Additionally, in order to get information on material performance at high temperature exposure, simultaneous TG and DSC analysis is done. The obtained data gives clear evidence on sandwich performance and proved its applicability in interior thermal insulation systems.

Abstract: Waste ceramic powder originating from the contemporary hollow bricks production is studied as a supplementary cementitious material in mortar composition. For the ceramic powder and cement, the measurement of chemical composition is done using XRF analysis. XRD device is used for the amorphous phase content measurement. The particle size distribution of ceramics and cement is accessed on a laser diffraction principle. Pozzolanic activity of ceramic powder was determined by the modified Chapelle test. The blended binder containing ceramic powder in an amount of 8, 16, and 24% of mass of cement is used for the preparation of mortars which are then characterized using the measurement of basic physical properties and mechanical properties. Among the basic physical properties, bulk density, matrix density and total open porosity are measured. The mechanical resistivity of mortars with blended binder is accessed by the compressive strength, flexural strength, and dynamic Young’s modulus measurement. Additionally, pore-size distribution of the developed mortars is analyzed using mercury intrusion porosimetry. Experimental data shows that an application of 24% waste ceramics in the blended binder provides sufficient mechanical resistivity of the mortar.

Abstract: Sodium silicate, usually known as water glass, is researched as material that can potentially find use in composition of cement based matrix in order to improve its porous structure and related physical parameters. The water glass is applied in cement paste mixture in an amount of 5, 10, 15, and 20 mass% of cement. The water dosage is experimentally accessed in order to attain the same workability of particular mixtures. For the applied water glass and cement, the particle size distribution is measured on laser diffraction principle. Pozzolanic activity of water glass is investigated using modified Chapelle test. The particular studied cement pastes are cured 28 days in water and characterized by basic physical and mechanical properties, whereas the results of mechanical resistivity are supported by pore size distribution data accessed by mercury intrusion porosimetry. Althought the particles of applied water glass are coarser than that of cement and did not exhibit pozzolanic activity, their application partially tightened the porous structure of hydrated products and thus contributed to the mechanical strength by means of filler effect. This makes good prerequisites for future research that will be focused on a development of new types of cement-based composites with incorporated sodium silicate used as an modifying admixture.

Abstract: An analytical approach to the determination of a varying salt diffusion coefficient is discussed. It is argued that the approach is fast and reliable and can be very convenient in various civil engineering applications dealing with the transport of salts in porous building materials. The advection-diffusion model of Bear and Bachmat is used to describe the salt transport, and the Bolztmann-Matano inverse analysis is applied to calculate the salt diffusion coefficient. Possible extensions to other models of transport are pointed out. The results are applied to a sandstone from the Msene quarry, Czech Republic.

Abstract: The in-situ examination of the historical enclosure wall of the Star Game Preserve located in the capital of the Czech Republic, Prague, is presented in the paper, in order to obtain necessary information for a qualified design of renovation and reconstruction treatments. At the visual inspection of the researched structure, the previous reconstruction methods are identified and evaluated, together with possible moisture sources. Moreover, the damage extent and propagation are assessed. Most of the oldest as well as newly constructed parts of the enclosure wall are found in bad condition and dilapidating. On this account, the building stone (arenaceous marl) forming the original historical masonry is examined to find compatible materials for the reconstruction works. Its chemical composition is accessed by X-Ray Fluorescence analysis. For the researched stone, basic physical, mechanical, hygric and thermal properties are measured. Using the obtained data, the proper material for reconstruction purposes will be identified.

Abstract: Several thermal insulation systems were developed for improvement of thermal performance of buildings. Exterior thermal insulation systems represent usually natural solution of the problem of low thermal resistance of building envelopes. However, in some cases, there is necessary to realize interior thermal insulation systems, what brings number of possible problems. Their common disadvantage is a limitation of interior space due to the thickness of thermal insulation layer and a possible condensation of water vapor which permeates the thermal insulation system. On this account, new sandwich composite with silica aerogel originally designed for application in interior thermal insulation systems is studied in the paper. Thermal properties are measured by two transient methods using devices ISOMET 2114 and RTB. The water vapor transport parameters are determined on the basis of dry cup and wet cup methods. The obtained data gives information on thermal and water vapor transport properties of the particular layers of sandwich composite and predetermines its behavior at real climatic exposure of building.

Abstract: Wider application of commercially produced phase change materials in production of building composites is limited due to their higher price and the inert polymer encapsulation which negatively affects mechanical parameters. This paper is focused on preparation of the composite material for energy savings. The phase change composite is prepared by soaking palm wax into the structure of diatomite powder using vacuum impregnation method. The compatibility of diatomite and palm wax in a newly developed PCM structure is investigated by FTIR spectroscopy. The improved thermal storage properties obtained by DSC analysis reveal melting temperature at 55.9°C and the phase change latent heat of 78.0 J/g. The laser diffraction based devise is used to determine the particle size distribution in order to assess the suitability of the developed wax/diatomite based composite for the cement based building materials. The obtained results indicate promising results from the point of view of improved latent heat storage at reasonable cost.

Abstract: A combined experimental/computational approach is applied for the determination of material parameters describing the transport of sulphate solution in porous structure of sandstone. The investigated sandstone, frequently used in historical buildings on the Czech territory, is chosen as a typical representative of stone masonry materials. At first, the moisture and sulphate concentration profiles in simulated 1-D water and sulphate solution transport experiment are measured. Here, the moisture content is determined by the gravimetric method, the sulphate concentration is measured by the ion chromatography. As a penetrating medium, 1M Na₂SO₄ water solution is used. The sulphate binding isotherm is experimentally accessed using the adsorption method. The experimental data are subjected to an inverse analysis assuming a diffusion-advection mode of sulphate transport. Finally, the moisture diffusivity for transport of Na₂SO₄ water solution, and the sulphate diffusion coefficient are calculated as the functions of moisture content and sulphate concentration, respectively.